Effect of Polymer Binders with Single-Walled Carbon Nanotubes on the Electrochemical and Physicochemical Properties of the LiFePO₄ Cathode

Abstract

We report the development of high-energy-density LiFePO 4 cathodes incorporating single-walled carbon nanotubes (SWCNTs) and a series of alternative polymer binders, including poly(3,4-ethylenedioxythiophene):poly(4-styrenesulfonate) (PEDOT:PSS), polyacrylonitrile copolymer (PAN), and sulfonated poly(2,6-dimethyl-1,4-phenylene oxide), which are processed through environmentally benign solvents. The binders ensured uniform distribution and excellent dispersion stability of the SWCNTs within the slurries, which resulted in enhanced electrical conductivities as compared to traditional polyvinylidene fluoride-bound composite cathode formulations. The characteristics of polymer−SWCNT composite binders were studied on cathodes with a high content of active material (95 wt % LiFePO 4 / C). Introduction of SWCNTs as low as 0.25 wt % into the slurry and the resultant composite cathode provided a good rate capability (beyond 110 mA h g −1 at 10 C charge/discharge rates). Among the composite binders studied and benchmarked, PEDOT:PSS− SWCNT composites with LiFePO 4 exhibited good electrical conductivity and rate capability at 10−50 C, while PAN−SWCNT composites exhibited better electrochemical stability and cyclability.

Engendering High Energy Density LiFePO4 Electrodes with Morphological and Compositional Tuning

“…Plate-shaped LFP microparticles were synthesized via a solvothermal route as we described earlier [25]. Spherical LFP particle agglomerates were provided by BTR New Energy Materials (Shenzhen, China).…”

“…Peeling tests were carried out on electrode samples with a length of at least 3 cm at a speed of 100 mm min −1 using a universal testing machine EZ-LX (Shimadzu Europa, Duisburg, Germany). The detailed procedure was reported earlier [25]. The peeling forces were normalized by the width of the peeling tape (1.9 cm).…”

“…Hence, SWCNT contributes to the overall peeling force of the electrode. To explain this fact, we analyzed electrode mechanical failure mechanisms using optical microscopy [25,49,50]. In each case, the peeled-off adhesive tapes contained a dark-colored layer of electrode material, while the peeled-off current collectors looked different depending on the electrode composition.…”

Electrochemically Active Polymer Components in Next-Generation LiFePO4 Cathodes: Can Small Things Make a Big Difference?

“…LiFePO4/CA/EAECP Cathodes In this type of composite electrodes, an auxiliary conductive additive (carbon black [90][91][92][93][94], single wall carbon nanotubes (SWCNTs) [80,95,96] or multi-wall carbon nano- Schema of the D3PIE method in dynamic growth with LiFePO 4 at the water/dichloromethane interface [89]. Reprint with permission from [89]; Copyright 2013, Elsevier.…”

“…In this type of composite electrodes, an auxiliary conductive additive (carbon black [90][91][92][93][94], single wall carbon nanotubes (SWCNTs) [80,95,96] or multi-wall carbon nanotubes (MWC-NTs) [94] is used in the electrode formulation to improve electron pathways between EAECP domains, lithium iron phosphate particles and the current collector. The addition of a CA is supposed to facilitate high rate performance of the composite cathode if the polymer displays limited electronic conductivity.…”